Man-made climate change is "unequivocal" and demands urgent action.
The IPCC's warning is stark: temperatures are likely to rise by about 3°C by 2100, with a range
of 2°C to 4.5°C.
The accelerated melting has increased to 0.6mm per year the contribution of Greenland’s
melting ice to rising sea levels. This represents a large proportion of the total sea level rise of
2mm-3mm a year that the world is experiencing.
The rise – the “best estimate” of the scientists from a range of predictions
between a rise of 2°C and 4.5°C – would be enough to put as many as 4bn extra people at risk
of serious water shortages. The extent of the temperature change is illustrated by the fact that the
difference between today’s world and the planet’s surface in the last ice age is only
about 5°C.
The latter would be close to the difference between the last ice age and today. Adaptation is
going to be part of the response, not least because a substantial rise in temperatures is already on
the way: the stock of greenhouse gases in the atmosphere is already 50 per cent above pre-industrial
levels. But it is also essential to mitigate growth in the stock, ideally to keep it below 550 parts
per million, which would still be double the pre-industrial levels.
Much depends, however, on the US, which is responsible for a quarter of all emissions. Without
willing American engagement, the chances of an effective international agreement are minimal. The US
does not have to sign a treaty. But it does need to put in place an effective scheme for emissions
control that can be linked to a global one.
This is a huge, long-term and global challenge that involves difficult questions of justice both
within and across generations. Humanity's ability to address it is a test of its capacity to manage
the consequences of its own actions. So far it has failed. It can afford to do so no longer.
